Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$138.71	8.802%	$150.9193	$150.92	$150.90	$150.90
Purchase #2	$238.97	12.176%	$268.067	$268.07	$268.05	$268.10
Purchase #3	$116.72	12.682%	$131.5224	$131.52	$131.50	$131.50
Purchase #4	$234.78	6.497%	$250.0337	$250.03	$250.05	$250.00
Purchase #5	$181.28	10.599%	$200.4939	$200.49	$200.50	$200.50
Purchase #6	$235.61	7.102%	$252.343	$252.34	$252.35	$252.30
Purchase #7	$228.46	10.280%	$251.9457	$251.95	$251.95	$251.90
7 purchase totals =	$1,374.53		$1,505.3250	$1,505.32	$1,505.30	$1,505.20